Make sure you always get the safest and most comfortable seat on any airplane. It's easy -just ask for it. When you book your flight, ask to sit in the first row (the bulkhead) or an exit row. You'll have plenty of leg room. Keep in mind that, in case of emergency, certain responsibilities come with an exit row seat.
If you don't think you can handle those responsibilities, choose an aisle seat in the row behind or in front of an exit row. That way, you'll have some leg room, and you're still close to an exit - but you won't have to open the exit door or direct people during an emergency.